It is known to produce rigid insulation plates allowing a considerably increased tension or pressure load compared to usual mineral wool mats in which the fibers extend in planes parallel to the main surfaces by using so-called strip insulation members of the above-mentioned kind in which the mineral wool strips are joined together at one main surface only by means of a plate of a hard material such as masonite or other pressed fiber board adhesively bonded to said main surface throughout the area thereof, said plate functioning, in addition as a pressure distribution plate.
These known rigid strip insulation plates have a considerably increased weight relative to plain mineral wool mats and their properties with respect to bending rigidity and breaking strength are limited to those of the hard connecting plate, the thickness of which must be small due to weight considerations. Moreover, since it is important that the strips which are secured to the hard plate only, are kept tightly together and not separated on the underside during manipulation of the insulation plates, these circumstances have resulted in that the known strip insulation plates have been manufactured in rather small dimensions only, up to about 60.times.90 cms., so that covering a greater surface area with such plates has required a great number of connecting points.
Since it is an advantage for the heat insulation properties that the mineral wool strips are pressed together before connection with the pressure distribution plate, the lack of connecting means at the underside may result in expansion of the strips, whereby the entire plate may bend.
Attempts to increase the bending rigidity and form stability of the known strip insulation plates by adhesively bonding hard plates to both main surfaces of the strip plate has not resulted in any improvement with respect to manipulation due to the increased weight, and has moreover led to increasing manufacturing costs.
For the production of pipe insulation mats it is also known to join mineral wool strips together by a flexible covering layer, made e.g. from paper, at one main surface.